The wheel bearing apparatus supports a wheel of a vehicle that freely rotationally supports a wheel hub that mounts a wheel, via a double row rolling bearing, are known for driving wheels and driven wheels. Due to structural reasons, the inner ring rotation type is used for driving wheels and both inner ring rotation type and outer ring rotation type are used for driven wheels. There are four generation types of the wheel bearing apparatus. In the first generation type, the wheel bearing includes a double row angular contact ball bearing etc. fit between a knuckle, forming a part of a suspension apparatus, and a wheel hub. In the second generation type, a body mounting flange or a wheel mounting flange is directly formed on the outer circumference of an outer member. In the third generation type, one inner raceway surface is directly formed on the outer circumference of a wheel hub. In the fourth generation type, the inner raceway surfaces are formed on the outer circumferences, respectively, of a wheel hub and an outer joint member.
Seals are mounted in the bearing portion to prevent leakage of lubricating grease sealed within the bearing and to prevent rain water or dusts from entering into the bearing from the outside. Recently, a maintenance free idea has been adopted in automobiles and thus it is desirable to further extend the operational life of the wheel bearing apparatus. Under the circumstances, it has been found, after the verification of damages from recovered bearings that the main causes of damage to the wheel bearings is due to sealing defects rather than peeling of structural elements of the bearing. Accordingly, it is believed that the operational life of the bearing can be extended by improving the sealability and durability of the seals of the bearings.
Various seals have been proposed to improve sealability. One example of a prior art wheel bearing apparatus incorporating such a seal is shown in FIG. 10. In the description below, the term “outer side” defines a side that is positioned outside of a vehicle body (left-hand side in drawings). The term “inner side” defines a side that is positioned inside of a vehicle body (right-hand side in drawings) when the bearing apparatus is mounted on the vehicle body.
The wheel bearing apparatus is a third generation type for a driven wheel. It includes an outer member 51 integrally formed with a body mounting flange 51b on its outer circumference. The flange 51b is to be mounted on a knuckle (not shown). Its inner circumference includes double row raceway surfaces 51a, 51a. An inner member 55 includes a wheel hub 53 formed with one inner raceway surface 53a on its outer circumference. The one inner raceway surface 53a is arranged opposite to one of the double row outer raceway surfaces 51a, 51a. A cylindrical portion 53b axially extends from the inner raceway surface 53a. An inner ring 54 is press fit onto the cylindrical portion 53b of the wheel hub 53. The inner ring 54 is formed with the other inner raceway surfaces 54a on its outer circumference. The other inner raceway surface 54a is arranged opposite to the other of the double row outer raceway surface 51a, 51a. Double row balls 57, 57 are freely rollably contained between the outer and inner raceway surfaces, via cages 56.
Hub bolts 52a are equidistantly arranged along the periphery of the wheel mounting flange 52. The inner ring 54 is axially secured relative to the wheel hub 53 by a caulked portion 58. The caulked portion 58 is formed by plastically deforming radially outwardly the end of the cylindrical portion 53b of the wheel hub 53. Seals 59, 60 are mounted on opposite ends of the outer member 51 to prevent leakage of lubricating grease sealed within the bearing and to prevent rain water or dusts from entering into the bearing from the outside.
As shown in an enlarged view of FIG. 11(a), an outer side seal 59 has a metal core 61 and a sealing member 62 integrally adhered to the metal core 61, via vulcanized adhesion. The metal core 61 includes a cylindrical press fit portion 61a press fit into the outer member 51. An inner portion 61b is bent radially inward from the press fit portion 61a and has a C-shaped cross-section.
The sealing member 62 is made of an elastic member, such as synthetic rubber, and is adhered to the inner portion 61b of the metal core 61. Its radially innermost end extends around the radially inner circumferential edge of the metal core 61. The sealing member 62 has radially inner and outer side lips 63, 64. The lips 63, 64 are bent radially outward and press against a ground surface of a base of the wheel mounting flange 52. The sealing member 62 further includes a radial lip 65 positioned radially inside of the inner portion 61b of the metal core 61. The lip 65 is adapted to press against a ground round corner portion 66 of a base portion of the wheel mounting flange 52.
In addition to the outer side seal 59, a shielding plate 67, forming an outside seal, is mounted on the outer side outer circumference of the outer member 51. The shielding plate 67 includes a cylindrical portion 67a, fit on the outer member 51, and an upstanding flange portion 67b. The plate 67 has a substantially L-shaped cross-section. The flange portion 67b is arranged opposite to the base end of the wheel mounting flange 52, via a predetermined gap, to form a labyrinth seal 68.
The labyrinth seal 68 prevents rain water or dusts from entering into the bearing. Thus, it is possible to have a sufficient sealing effect if the interference of the side lips 63, 64 of the outer side seal 59 is set small to reduce the rotational torque caused by the contact of the seal 59 against the wheel hub 53 and to contribute to improve fuel consumption (see Japanese Laid-open Patent Publication No. 147298/2005).